As known in the art, to breakdown a stack of stacked and stickered lumber (hereinafter referred to as a lumber stack), a lumber stack arrives on an infeed transfer chain, which places the lumber stack over a rotatable hoist frame which has been rotated up-right to receive the lumber stack, where once the lumber stack is positioned over the hoist arms, the hoist is rotated back to an incline, where the hoist then lifts the lumber stack up the inclined surface formed by the inclined hoist frame, so as to discharge under the force of gravity rows or tiers of individual pieces of lumber from the top of the lumber stack, as the top of the lumber stack is pushed beyond the uppermost end of the frame.
It is also known to assist lifting the lumber stack towards the uppermost end of the frame so as to discharge tiers of lumber from the stack by providing secondary lumber stack support arms which at some intermediate transfer point take over the upward translation of the lumber stack from the primary lumber stack support arms on the rotatable frame.
In particular, applicant is aware of U.S. Pat. No. 4,838,748 which issued on Jun. 13, 1989 to Johnson for a device entitled "Hoist and Accumulator Anm Apparatus". Johnson teaches a rotatable hoist frame for rotating a lumber stack, from an upright position into an inclined position flush with an accumulator arm apparatus. Hoist frame hoisting support members translate up the incline to slide the load of tiered material upwards onto a similarly inclined frame surface on the accumulator arm apparatus. Retracted accumulator arms in the accumulator arm apparatus extend upwardly from under the inclined frame surface, once the load of tiered material has been slid from the hoist frame onto the accumulator arm apparatus. The accumulator arms take over from the hoist frame horizontal supports and slide the partial lumber stack further upwards to a discharge point at the uppermost edge of the accumulator arm apparatus. The accumulator arms then retract and are repositioned ready to accept the next partial lumber stack which has been transferred up the hoist frame.
Also, applicant is aware of Swedish Patent 392,453 which issued on Mar. 28, 1977 to Hellstrom, for a device entitled "Arrangement for Feeding of a Package of Goods Such as a Package of Lumber". This apparatus is similar in operation to the Johnson apparatus. However, the secondary accumulator apparatus is mounted above the inclined face, and extends down under the partial lumber stack to take over the translation from the lower hoist frame.
Also, applicant is aware of U.S. Pat. No. 5,249,915 which issued on Oct. 5, 1993 to Ritola for a device entitled "Dual Independent Hoist Breakdown Station". This apparatus accomplishes similar lumber stack breakdown operation as the above devices, with accumulator arms being used for both primary and secondary hoists. There is also an additional tilting frame needed, that rotates up to receive the lumber stack and then rotates back against the inclined face where the primary accumulator arms are extended under the lumber stack to begin translating of the lumber stack up the inclined face.
It is also known in the industry that some long loads of lumber (particularly long thin lumber) can hang up on the unsupported end causing the lumber to come off the tilt hoist skewed and then bunched up, where the operator would then have to shut down the tilt hoist and the outfeed transfer and then unscramble the lumber by hand before restarting the outfeed transfer and tilt hoist.